The invention relates to a heat exchanger with tubes and with an end piece which has a tube plate comprising a plurality of individual plates.
A heat exchanger of this type is described, for example, in EP 0 563 471 A1. The heat exchanger disclosed by that document is designed as a two-row flat-tube evaporator which has two flows of medium passing through it. Corrugated fins which have ambient air flowing over them are located between the flat tubes. The refrigerant first of all flows through the rear row of flat tubes, as seen in the main direction of flow of the air, from the top downward and is then collected and diverted, by means of a diverter device, in the opposite direction to the direction of flow of the air, entering the first, i.e. front row of flat tubes, through which it flows from the bottom upward. With this design, therefore, the refrigerant is diverted over the depth, i.e. counter to the direction of flow of the air. As a result, the flow paths for the refrigerant in each case comprise two sections, with each section corresponding to a tube length. The refrigerant is distributed and collected by a collection and distribution device, which is formed by a multiplicity of plates which are layered on top of one another and are soldered together. These plates substantially comprise a base plate, a distributor plate above it, with a partition running in the longitudinal direction, and a cover plate with feed and discharge openings for the refrigerant. In a similar way, the diverter device arranged on the opposite side is composed of individual plates. This results in a low overall height of this evaporator. In addition, there is optionally what is known as a stop plate, which is in each case laid onto the base plate and forms a stop for the tube ends. One drawback of this type of evaporator is that the refrigerant, on account of the distribution or collection chamber extending over the entire width of the evaporator, is distributed unevenly to the individual tubes. Furthermore, the two-row design requires increased assembly outlay.
What is known as a divider plate with individual openings for distributing the refrigerant between the individual tubes has been proposed for a similar evaporator in EP 0 634 615 A1. This results in more uniform distribution of the refrigerant to the tubes, but this is at the expense of an increased number of plates and therefore higher outlay on materials and assembly.
U.S. Pat. No. 5,242,016 describes an evaporator with refrigerant distribution through passages in a large number of plates, which likewise contribute to a more uniform distribution of the refrigerant between heat-exchanger tubes. However, this requires a very large number of plates and high manufacturing costs.
DE 100 20 763 A1 has disclosed a further design of evaporator, which is intended for operation with CO2 as refrigerant and in which a pressure-resistant collector housing is to be achieved by virtue of the fact that a multiplicity of plates provided with apertures are stacked on top of one another and soldered together. This evaporator is of one-row design, specifically with multi-chamber flat tubes through which medium flows both upward and downward, which is made possible by a diverter device located at the lower end of the tubes. One drawback of this design of evaporator is the large number of plates with relatively narrow passages, which firstly entails additional weight and secondly involves the risk of the passages in the collector housing being closed up during soldering, i.e. becoming blocked by solder.
EP 1 221 580 A2 has described an evaporator for a fuel cell system, which comprises a header piece which includes a base plate and a cover plate secured to it. Fuel passes via a connection part into a fuel distributor chamber, and from there into guide passages and via apertures in the base plate into heat-uptake passages of the evaporator. In this fuel evaporator, there is a small number of plates in the header piece, but these plates are highly complex to manufacture. Moreover, supply of fuel to the heat-uptake passages is very uneven depending on the pressure distribution in the fuel distributor chamber and in the guide passages.